One such prior art relay is described in U.S. Pat. No. 4,455,650. The device described in said document comprises a receiver which is normally in service, a transmitter suitable for transmitting a pulse throughout the duration of a pulse received by the receiver, and timed switching means for switching off the receiver for a period of time which is longer than the duration of each pulse.
The information relay system comprises a relay-by-relay series of devices of the type described above, each comprising a transmitter and a receiver tuned to the same carrier frequency, together with means for preventing the receiver from receiving as soon as the transmitter is switched on. Each device can thus receive information coming from another device and can relay this information towards a further device which has not received it.
This device has the undoubted advantage, in particular, of preventing interference between the various relay systems, thereby enabling an entire series of information pulses to be relayed without portions thereof being omitted.
However, under certain circumstances, the use of such a device can be disturbed, e.g. by interference pulses if they are of duration greater than the value of the time constant during which the receiver is switched off. If the receiver does receive a pulse of duration longer than said time constant, then when the time constant has elapsed, the receiver is switched back on and perceives the remainder of the interference pulse as a pulse in a train to be relayed, and this continues until said interference pulse stops being transmitted. As a result the associated receiver outputs a series of secondary pulses corresponding to the continuous interference pulse being split up into a plurality of pulses. It goes without saying that in a complex relay system comprising a plurality of devices constituting a whole, transmitting such secondary pulses in response to interference pulses can completely disturb the information relay system as a whole since the information becomes erroneous and therefore unusable.
The object of the present invention is to provide a device for mitigating the above-mentioned drawbacks.